The tracking of parts and products in a manufacturing operation requires a means of marking or labeling them in order that they can be readily and accurately identified and tracked. In the steel industry, the parts or products are often labeled at temperatures well above ambient temperature, e.g., at temperatures above about 400.degree. C. This necessitates the use of markings or labels which can be attached and will maintain their integrity at such temperatures. High temperature-resistant paint, crayon, and chalk are currently used for marking hot steel coils, but these markings are generally handwritten, can degrade with time, and thus may not be consistently legible. Moreover, such markings are not machine-readable and thus are not adaptable to computer scanning and tracking methods. Although heat-resistant metal tags can be imprinted with machine-readable bar codes, the tags currently require attachment by mechanical means such as nails, rivets, or screws, which can cause damage to the substrate. Wire attachment of the metal tags is also possible. However, the wire is apt to be broken off during handling, causing the tag to become disconnected from the part. U.S. Pat. No. 4,301,726 (Sato et al.) describes a stencil method for marking hot material, but this method tends to be cumbersome and expensive. Thus, there is a need for a high temperature-resistant label which is conveniently and durably attachable, and which is capable of displaying machine-readable bar codes or other such printed information.
Heat-resistant labels have been described which use various different types of adhesives, including pressure-sensitive adhesives (PSAs), as the means for attachment to a part. PSAs enable easy label attachment but do not possess sufficient high temperature stability for certain applications.
Japanese Patent Application No. 2-131931 (FSK K.K.), published May 21, 1990, describes a ceramic label which is said to be useful as a display label under high temperature conditions. The ceramic label is characterized as a paper-form material which is coated with a mixture of a pressure-sensitive adhesive and an oxide solder composed of oxides such as PbO, ZnO, or B.sub.2 O.sub.3.
U.S. Pat. No. 5,008,151 (Tominaga et al.) discloses a glass powder adhesive sheet which can be used as a heat-resistant label. This glass powder adhesive sheet comprises a glass powder molding layer comprising a glass powder, a resin binder, and, if necessary, inorganic powder and/or metal powder, and an adhesive layer having a thermal decomposition initiation temperature higher than that of the resin binder. The preferred materials for the adhesive layer are those having pressure-sensitive adhesive properties at room temperature.
A welding backup tape is described in U.S. Pat. No. 3,372,852 (Cornell). The tape comprises a backing coated with adhesive, preferably a heat-resistant pressure-sensitive adhesive, and having a flexible strip of refractory material adhered to a central portion of the adhesive-coated side of the backing. The refractory material comprises refractory particles and an organic binder. During a welding operation, the refractory strip is positioned over the seam to be formed and functions as a backing means which has very good heat resistance and which is sufficiently gas permeable to permit gases produced in the welding operation to escape therethrough. The tape can be removed readily from the metal after the welding operation is completed.
Both metal and glass have been used in various types of applications for bonding to metal and ceramic surfaces. For example, the Encyclopedia of Materials Science and Engineering, Volume 3, pages 1958-65, The MIT Press (1986), states that oxide mixtures such as glass are widely used as bonding agents for joining ceramics and for forming ceramic-to-metal seals in the fabrication of electron tubes, magnetic recorder heads, high-pressure alkali vapor lamps, and high-voltage feedthroughs.
U.S. Pat. No. 3,175,937 (Bayer et al.) describes a method of bonding metals using compositions comprising glass powder, a compound which is capable of supplying metal ions to the glass, and/or an oxidation-resistant metal powder.
U.S. Pat. No. 3,615,276 (Singleton) discloses a protected metal article comprising a core of sheet steel which is coated with a protective metal consisting essentially of zinc and which has a fibrous glass cloth impressed into the protective metal coating.
U.S. Pat. No. 3,669,787 (Cornell) describes a flexible, deformable self-supporting glass frit sealing tape useful in joining glass or other inorganic substrates. The tape comprises a sheet material formed from glass frit bonded with a minor amount of heat-depolymerizable rubbery polymer, preferably coated on one or both surfaces with a small amount of similarly depolymerizable pressure-sensitive adhesive.